This invention relates to an improved method of hydrolyzing hydridosilanes with 2 or more hydrolyzable groups to form polymers, said method comprising forming an arylsulfonic acid hydrate containing hydrolysis medium, adding the silane to the hydrolysis medium, facilitating hydrolysis of the silane to form the polymer, settling the hydrolysis medium and polymer into an acid layer and an organic layer containing the polymer, separating the organic layer from the acid layer, contacting the organic layer with a neutralizing agent, and separating the organic layer from the neutralizing agent.
The polymers formed by the above process have excellent coating and sealing characteristics when cured to their ceramic or ceramic-like state. Most recently such polymers have found particular utility in coating electronic devices to form protective barriers. See for example Haluska et al., U.S. Pat. No. 4,756,977.
It is well known in the prior art that halosilanes readily hydrolyze in the presence of water to form silanols which condense to form polysiloxanes. Furthermore, it is well known that these two processes occur almost simultaneously when the halosilane contains three or more halogen atoms. The result of this rapid hydrolysis and condensation is an insoluble gel which is of little practical value. See eg. Boldebuck, U.S. Pat. No. 2,901,460.
Numerous solutions to the above problem have been suggested. Boldebuck described above, for instance, utilizes a hydrolysis medium comprising tetrahydrofuran and water in an attempt to alleviate the gelling. It is disclosed therein that the use of a chlorosilane with this medium results in the formation of a hydrolysate which spontaneously separates. The resultant hydrolysates are subsequently washed with water and heated to form a hard resinous polysiloxane.
U.S. Pat. No. 3,489,782 granted to Pruvost et al. discloses a process for hydrolyzing silanes which comprises dissolving the silane in a polar solvent, hydrolyzing the silane in a single liquid homogenous phase and separating the hydrolysate from the secondary reaction products. It is disclosed therein that the separation may be accomplished by neutralization with a base or by washing with water and subsequent neutralization. This reference, however, does not disclose the use of a hydrolysis medium comprising an arylsulfonic acid hydrate or the step of washing the organic phase with sulfuric acid and then neutralization with a base.
U.S. Pat. No. 3,615,272 granted to Frye et al. describes a process for forming hydrogensilsesquioxane resin comprising reacting a silane in a hydrocarbon solvent with sulfuric acid and an aromatic hydrocarbon, washing the reaction mixture with water and sulfuric acid until neutral and recovering the product by evaporating the solvent. Nowhere does this reference describe the use of a mild base to neutralize the organic phase. Furthermore, numerous difficulties developed when scale-up of the above process was attempted.
It has now been unexpectedly found that the process of the present invention provides an improved commercially viable process for the synthesis of hydrocarbon soluble siloxane resins.